Computer systems often contain a storage device such as a disk drive. FIG. 1 shows a typical architecture of a disk subsystem A disk drive subsystem can be described as a system of disk platter(s); analog read channel and write channel circuitry; an encoder/decoder; a servo engine including a mechanical mechanism to position the read/write heads on the disk platter(s) and an electronic mechanism to control the head position; a local microprocessor (sometimes referred to as a local microcontroller); local processor memory; buffer memory; and disk drive controller circuitry. It is the task of the disk drive controller to interface with the host central processor or microcomputer and correctly read and write user data onto the disk.